This invention relates to radio navigation systems employing directional radio signals, and more particularly to radio guidance systems which are especially useful for aircraft.
In radio navigation systems for providing guidance signals, it is common to provide guidance signals which simply define a desired approach direction to a landing runway. However it is very desirable to provide precise directional "bearing" and glide path elevation information to an aircraft approaching an airport from any direction which gives the aircraft its precise angle of approach to a ground based transmitter at the airport. For azimuth, this requires 360.degree. azimuth signal coverage. Providing 360.degree. azimuth coverage with a high accuracy of signal resolution usually presents formidable problems, including potentially high cost and elaborate antenna structures.
Accordingly, it is one object of the present invention to provide a very accurate guidance signal which is available over a wide angle, and which may encompass the entire 360.degree. of azimuth with a high resolution and with a simple and very economical structure.
Furthermore, providing wide angle azimuth coverage in a dependable and reliable manner is also complicated by difficulties in monitoring the signals produced by the system in order to be certain that accuracy is maintained within required limits.
Accordingly, it is another object of the invention to provide a system for wide angle azimuth radio guidance which is very simply and economically monitored.
Further objects and advantages of the invention will be apparent from the following description and the accompanying drawings.
The invention is carried out by a method of providing accurate azimuth orientation information to an aircraft in any azimuth angle position over a wide angle sector with respect to a ground station comprising mechanically rotating about a vertical axis a ground station transmitter antenna array which is capable of producing directional radio guidance signals by an electrical scan through only a limited azimuth angle sector for each rotational position thereof, transmitting radio guidance signals from the antenna array in a sequence of separate electrically scanned sector signals during successive mechanical rotation through a plurality of separate rotational positions, and transmitting radio signals in conjunction with each of said electrically scanned sector signals to uniquely identify the rotational position of said antenna array, corresponding to a particular sector, the number of said separate rotational positions at which electrically scanned sector signals are emitted being sufficient to cover all azimuth angles within said wide angle sector by the combination of all of the separate electrically scanned sector signals.